JPS631394B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for setting a plating current to achieve a predetermined plating amount in continuous electroplating of metal strips.

Prior Art Plating current control in conventional continuous electric plating is set according to the relationship that the plating current is proportional to the product of the width and speed of the strip to be plated and the amount of plating deposited, and the operation is performed at this set current value. This was done by modifying the set current value based on the actual measurement results of the plating amount. However, in the conventional control described above, the plating current is set and corrected by focusing only on the total value of the currents supplied to each of the plurality of electrodes installed along the strip passing direction. However, the current density of the electrodes was not considered.

However, according to the research of the present inventors, the current density of the electrode in continuous electroplating affects the quality of the plating layer (especially the composition of the plating layer), and the appropriate current density range to obtain a predetermined plating layer quality is It has become clear that the current density exists, and that it is essential to consider the current density when setting and modifying the plating current, since this current density also affects the plating current efficiency.

Further, when setting the plating current value, it is also necessary to set the total plating current and distribute it to each electrode so that the current value for each individual electrode is within the allowable limit.

Purpose of the Invention Based on this knowledge, an object of the present invention is to provide a method for setting a plating current so as to achieve a predetermined plating amount while ensuring a predetermined plating quality.

Components and Functions of the Invention In the continuous electroplating of metal strips, the method of the present invention is to calculate the calculated plating current by multiplying the actual plating amount, the strip width, and the strip speed and dividing the result by the electrochemical equivalent. When defining, the relationship between the plating current efficiency defined by the ratio of the calculated plating current value and the actual plating current value, the stripping speed, and the current density, the plating current value, the plating amount, the stripping speed, the strip width, and the plating Two relational equations with the current efficiency are determined in advance, and the above two equations are calculated using the target plating amount, the stripping speed setting value, and the stripping width.
The required plating current value is calculated from the following relational expressions, and when the calculated plating current value is within the permissible limit determined by the electrode, the calculated plating current value is used as the set value, and when the calculated plating current value is outside the permissible limit, the plating current value is set as the set value. The present invention is characterized in that the set plating current value is set to a value within an allowable limit, and the stripping speed corresponding to the set plating current value is calculated from the above two relational expressions to correct the stripping speed set value.

The present invention will be explained in detail below. First, two relational expressions used in the present invention will be explained. It was previously stated that the plating current in electroplating is proportional to the product of the strip width and speed and the amount of plating deposited, and this can be expressed as the following equation.

I _T = Ic / η = W・V・C _T /η・1/k ...(1) where I _T : Actual plating current [A] I _c : Calculated plating current [A] η : Current efficiency W: Strip width [m] V: Strip speed (line speed) [m/
sec] C _T : Actual plating deposition amount [g/m ² ] k (=K/F): Electrochemical equivalent [g/coulomb] where F is Faraday's constant K is a constant determined by the standard composition of the plating layer Conventional plating current In the control, first, an appropriate value determined empirically is used for the current efficiency η, and the target value of the plating adhesion amount and the set value of the stripping speed are set as described above.
Calculate and set the required plating current value by substituting it into equation (1), and measure the plating amount after plating while plating with this set plating current value, and then measure the difference between the actual plating amount and the target value. Alternatively, a method has been used in which the plating current is corrected by correcting the current efficiency assumed at the beginning using the ratio. On the other hand, the present inventors have proposed that, as mentioned above, the current density of the electrode affects the quality of the plating layer, and therefore the current density should be set within a certain range in order to obtain a predetermined plating layer quality. , and this current density also affects the current efficiency, and from the knowledge that the current efficiency is also affected by the stripping speed, the following relational expression was obtained based on experiments.

η=a ₀ +a ₁・D _K +a ₂・V ……(2) However, D _K = 1/100・I/W・N・L ……(2′) Here, D _K : Current density [A/dm ² ] I: Total plating current [A] N: Number of electrodes used L: Length of one electrode in the strip passing direction [m] a ₀ , a ₁ , a ₂ : constants And in the present invention, the plating current In setting the value, first determine the current density range that can ensure the predetermined plating layer quality according to separately determined standards, and under the condition that the current density D _K is within the predetermined current density range, The required plating current value is calculated from the above equations (1) and (2) using the plating adhesion target value, strip speed setting value, and strip width. When this calculated plating current value is within the allowable limit determined by the electrode, this calculated plating current value is set as the initial plating current value. The permissible limits determined by the electrodes are predetermined as follows. In other words, normally in continuous electroplating equipment, a large number of electrodes are installed in the strip passing direction, sandwiching the strip passing through the plating tank, and each electrode, including the rectifier, is designed under the same conditions. Due to variations in each electrode due to deterioration over time, the limit (upper limit) of the supply current for each electrode is not necessarily the same. Therefore, the total plating current is determined by the upper limit of each of the N electrodes that are energized during the operation. Must be within the total value of Therefore, when the calculated plating current value is outside the permissible limit determined by the electrode, the plating current value to be actually initially set is a value somewhat lower than the permissible limit value, that is, the sum of the individual upper limits of the N electrodes. (a value that takes into account the correction allowance for the set plating current value in response to variations in stripping speed, which will be described later), and then convert this set plating current value to the plating current value (I _T or I) in equations (1) and (2) above. The strip speed is calculated inversely from both equations by substitution, and the calculated strip speed is set again as a set value.

Then, during operation with this set plating current value, measure the stripping speed and set an appropriate period (for example, 100
(1) above,
The required plating current value is recalculated by substituting it into the stripping speed (V) in equation (2), and the previous plating current value is corrected.

Example Next, examples will be described.

FIG. 1 is a diagram showing an example of an apparatus configuration for implementing the present invention. In the figure, 1 is a plating tank (electrogalvanizing in this example), 2-11, 2
-12, . . . 2-n1, 2-n2 are electrodes arranged to sandwich the strip S, which is the material to be plated. 3 is a current distribution circuit that distributes plating current to each electrode (including a rectifier not shown). 4 is the setting device (or host computer) 5
Using the target value of plating adhesion amount, strip width, strip speed setting value, number of electrodes used, current allowable limit value, etc. set from , and the actual strip speed value input from the speed detector 6, equation (1) is calculated. This is an arithmetic circuit that calculates the initial setting value of the plating current, the corrected value of the stripping speed, and the corrected value of the plating current from the equation (2). A speed control circuit 7 controls the strip speed based on the strip speed correction value calculated by the arithmetic circuit 4.

FIGS. 2a and 2b are flowcharts showing an example of the calculation flow in the calculation circuit 4 of FIG.
Figure a shows the calculation flow for the initial set value of the plating current, and Figure 2 b shows the calculation flow for the plating current correction value when modifying the plating current according to fluctuations in the stripping speed during operation with the set value. . When calculating the plating current setting value, first calculate the constant A (=W・C _A /k) from the strip width (W), the target value of plating adhesion amount (C _A ), and the electrochemical equivalent (k). Also, calculate the constant B (=1/100·W·L) from the strip width (W) and the length (L) of the electrode in the strip passing direction. On the other hand, the formula for calculating the required plating current (I _P ) is obtained by combining equations (1), (2), and (2') above (as C _T →C _A , I _T , and I → I _P ). is determined and set in the arithmetic circuit 4, and the first
By substituting the strip speed setting value (V _P ) given from the setting device 5 in the figure for V in the above equation (3), and substituting the number of electrodes used (N _P ) for N in the above equation (3), the above calculation is performed. Using values A, B and predetermined constants a ₀ , a ₁ , a ₂
Calculate the required plating current (I _P ) from equation (3). The number of electrodes used (N _P ) to be substituted into the above equation (3) is calculated from the above equation (2) using the approximate predicted value of the total plating current value, and is determined to be within the current density range that can ensure the predetermined plating layer quality. Find the number of electrodes used and use this as the set value for the number of electrodes used. When the required plating current (I _P ) calculated from the equation (3) is within the allowable limit (Imax) determined by the electrode, the calculated plating current (I _P ) is set in the current distribution circuit 3 of FIG. The current distribution circuit 3 distributes the total plating current to each electrode. Said (3)
When the required plating current (I _P ) calculated from the formula exceeds the allowable limit (Imax), the allowable limit (Imax) is set as an initial setting value in the current distribution circuit. In this case, the strip speed calculation formula obtained from equations (1), (2), and (2') above is The strip speed Vs obtained by substituting Imax for I and N _P for N is set as a corrected setting value in the speed control circuit 7 of FIG.

The above-mentioned calculation of the initial set value of the plating current is performed whenever any one of the strip width, the target value of the plating adhesion amount, and the set value of the stripping speed changes. The next correction value for the plating current is calculated by calculating, for example, 100% during operation with the plating current at the initial setting value.
Every ms, the actual velocity value (Va) input from the velocity detector 6 in Fig. 1 is substituted into V in the above equation (3), and N in equation (3) is the actual electrode value at that point. Substitute the number of uses (Na) to calculate the corrected value of the required plating current. If the calculated plating current is within the allowable limit, set it as the corrected set value; if it exceeds the allowable limit, use the same procedure as for initial setting to set the corrected set value within the allowable limit and set the stripping speed. Modify the value. In this way, the plating current is set and modified in consideration of the current density of the electrode. Furthermore, as mentioned above, the current efficiency during operation η
actual value of current density D _K (calculated backwards using the actual plating current from equation (2') above), and stripping speed V Based on the measured values of , the constants a ₀ , a ₁ , and a ₂ in equation (2) above can be determined by a learning method using the Kalman filter method.

Effects of the Invention As described above, in the continuous electroplating of strips, the method of the present invention takes into account the current density that affects the quality of the plating layer and the current efficiency, and also sets the plating current by taking into account the current permissible limit of each individual electrode. Therefore, the amount of plating deposited can be controlled within a predetermined range while ensuring a predetermined plating quality and without setting a current that exceeds the permissible limit for each electrode.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a device configuration in an embodiment of the present invention, and FIGS. 2a and 2b are flowcharts showing a specific example of a control flow in the present invention. 1: plating tank, 2-11 to 2-n2: electrode,
3: Current distribution circuit, 4: Arithmetic circuit, 5: Setting device (or host computer), 6: Speed detector, 7: Speed control circuit.

Claims (1)

[Claims] 1. In continuous electroplating of metal strips,
When the calculated plating current is defined as the result of multiplying the actual plating amount by the strip width and stripping speed and dividing by the electrochemical equivalent, Ic=C _T・W・V/k...(1) Here, Ic: Calculated plating current C _T : Actual plating deposition amount W: Strip width V: Stripping speed k: When defined as electrochemical equivalent, plating current efficiency defined as the ratio of the calculated plating current value to the actual plating current value The relational expression between , strip speed, and current density is: η=a ₀ +a ₁・D _K +a ₂・V ……(2) However, D _K =1/100・I/W・N・L Here, η: Plating current efficiency D _K : Current density I: Total plating current N: Number of electrodes used L: Length of one electrode in the strip passing direction V: Stripping speed W: Strip width a ₀ , a ₁ , a ₂ : Constant and the relational expression between plating current value, plating deposit amount, stripping speed, stripping width, and plating current efficiency, i.e., I _T =C _T・W・V/η・1/k ……(3) Here, I _T : Actual plating current C _T : Two relational expressions (2) and (3) for plating adhesion amount are determined in advance, and using the target plating amount, stripping speed setting value, and stripping width, the above-mentioned 2. Calculate the required plating current value from the two relational expressions, and if the calculated plating current value is within the permissible limit determined by the electrode, use the calculated plating current value as the set value, and if the calculated plating current value is outside the permissible limit. A continuous electroplating method characterized in that the set plating current value is set to a value within an allowable limit, and the stripping speed corresponding to the set plating current value is calculated from the above two relational expressions to correct the stripping speed set value.